1999 Spotlight on Graduate and
Undergraduate Research at ESF
AN ASSESSMENT OF CARBOHYDRATE PERMETHYLATION AND DEVELOPMENT OF A NOVEL ACID-CATALYZED APPROACH. Jeremy Bartholomew and Neil Price.
QUANTUM CHEMICAL ANALYSIS OF THE REACTION HS + NO2. Ted Dibble and Shane Lewis.
A BIOMIMETIC SYNTHESIS OF A NATURAL INSECTICIDAL ORTHOESTER. Juan Faraldos and Jose-L Giner.
THE EFFECTS OF NITROGEN SOURCE ON PSP TOXIN FORMATION IN THE TOXIC CYANOBACTERIUM, APHANIZOMENON FLOS-AQUAE. Gregory G. Goddard, Michael F. Satchwell, and Gregory L. Boyer.
PROGRESS IN THE DEVELOPMENT AND APPLICATION OF TOPOCHEMICALLY MODIFIED CELLULOSE NANOCRYSTALS. Maren Grunert and William T. Winter.
LINEAR-DENDRITIC BLOCK COPOLYMERS AS NOVEL ENCAPSULATOIN AGENTS FOR POLYCYCLIC AROMATIC HYDROCARBONS. Kevin R. Lambrych and Ivan Gitsov.
STEROL BIOMARKERS FOR RED TIDE AND BROWN TIDE ALGAE. Xiaoyong Li, Juan Faraldos and Jose-L Giner.
TEMPERATURE CALIBRATION FOR EXTRACTION OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) BY P.I.S.C.E.S. PASSIVE IN-SITU CONCENTRATION EXTRACTION SAMPLER . Matt Lochansky, Jocelyn Polito, Dr. John Hassett.
MIREX AND PHOTOMIREX DYNAMICS IN LAKE ONTARIO. Kelly A. Lowe and John P. Hassett.
ACTION SPECTRA FOR PHOTOCHEMICAL PRODUCTION OF HYDROGEN PEROXIDE IN NATURAL WATERS. Gary W. Miller and David J. Kieber.
METABOLIC MARKERS FOR THE DETECTION OF IRON LIMITATION IN THE BROWN TIDE ALGA, AUREOCOCCUS ANOPHAGEFFERENS. Michael F. Satchwell, Darlene B. Szmyr, Jeffrey A. Alexander, and Gregory L Boyer.
LASER SPECTROSCOPY OF ALKOXY RADICALS AS A TOOL FOR ATMOSPHERIC CHEMISTRY. Liat G. Shemesh, Wei Deng, David R. Katz, Michael D. Lilien, Chuji Wang, and Theodore S. Dibble.
THE PRODUCTION OF ACTIVATED CARBON AND CARBON PAPER FOR DOUBLE LAYER CAPACITORS AND FUEL CELLS. Han Liu, Suoding Li, Prithwiraj Maitra and Prof. Israel Cabasso.
STRUCTURE AND BIOSYNTHESIS OF TUNICAMYCINS AND CORYNETOXINS. Billyana Tsvetanova and Neil Price.
DEVELOPING AN ELISA ASSAY TO DETERMINE THE CONTENT OF FERRICROCIN IN SOILS. Tzu-Pin Wang and Gregory L. Boyer.
NEW ASPECTS IN ELECTROCHEMICAL SYSNTHESIS OF POLYSILANES. Xinwei Wang, Youxin Yuan and Prof. Israel Cabasso.
D-MANNOSE/L-FUCOSE METABOLISM IN RHIZOBIUM BACTERIA. Tong Zhang and Neil Price.
BINDING PEPTIDE IN RESPONSE TO ALUMINUM BY THE MYCORRHIZAL PRODUCTION OF A METAL FUNGUS WILCOXINA MIKOLAE. Guozhang Zou, Michael F. Satchwell, Jonelle Penschow and Gregory L. Boyer.
AN ASSESSMENT OF CARBOHYDRATE PERMETHYLATION AND DEVELOPMENT OF A NOVEL ACID-CATALYZED APPROACH. Jeremy Bartholomew and Neil Price, Chemistry Department, 338 Jahn Lab, SUNY- College of Environmental Science and Forestry, Syracuse, NY 13210.
Hakormori permethylation analysis is a classical procedure for micro-scale linkage analysis of carbohydrate and glycoconjugates. The procedure typically involves a methylating agent (methyl iodide or dimethylsulfate) and a strong base catalyst (sodium hydroxide or sodium hydride) in the presence of dimethylsulfoxide solvent. While this gives efficient and complete methylation of sugars, the strong basic conditions can cleave functional groups such as esters. An alternative permethylation procedure is being investigated, using the reagent methyl trichloroacetimidate. Acid catalyzed (trifluoroacetic acid or boron trifluoride:etherate) and non-catalyzed reaction, and solvent conditions is being assessed. Model compounds D-glucose and lactose have been permethylated by the classical procedure and our newer method. The results are compared by gas chromatography (GC) , and by gas chromatography-mass spectroscopy (GC-MS) in electron impact mode. This novel procedure holds considerable promise for the analysis of base labile glycoconjugates.
This study investigates the possible states of the species in a reaction between HS* radicals and NO2. This reaction serves as a model for atmospheric reactions of HS*, as there are many possibilities involving the HS* radical. HSO and NO have been experimentally been observed as products, but others may also be formed. We want to see if HSONO or HSNO2 can be products, and look at how other products might be formed from HSONO. Since HSONO and HSNO2 have not been observed experimentally, we use computational chemistry to determine their stability. The programs Gaussian 94 and 98 computed the data using the density functional theory.
Petuniasteroids are steroidal orthoesters isolated from the aereal parts of Petunia species. These compounds are potent insecticides against lepidopteteran larvae such as Heliothis zea with ED50's as low as 2 ppm. The bicyclic orthoester system on the steroidal side chain has been shown to be essential for insecticidal activity. We have developed an efficient synthesis of petunisteroids. This synthesis features a reaction that produces the bicyclic orthoester in a fashion mimicking the natural biosynthetic process. This biomimetic reaction occurs under very mild acidic conditions, is exceptionally facile and proceeds in near quantitative yield. We have completed the synthesis of Petuniasterone D using this methodology.
THE EFFECTS OF NITROGEN SOURCE ON PSP TOXIN FORMATION IN THE TOXIC CYANOBACTERIUM, APHANIZOMENON FLOS-AQUAE. Gregory G. Goddard, Michael F. Satchwell, and Gregory L. Boyer, Faculty of Chemistry, State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210 USA (firstname.lastname@example.org, email@example.com)
Aphanizomenon flos-aquae NH5 is a nitrogen-fixing cyanobacterium that produces the neurotoxins saxitoxin and neosaxitoxin. To investigate the effect of nitrogen source on toxin production, axenic cultures of A. flos-aquae were grown in 2.4 batch cultures using defined media with or without added nitrate. Cells were monitored three times per week for in vivo fluorescence, rates of nitrogen fixation, ratio of heterocysts to vegetative cells, and PSP toxin production. Cells grown without added nitrogen (e.g. fixing atmospheric N2 for growth) grew slightly better than those cultures with added nitrate. Both treatments (with and without added nitrate) showed similar rates of nitrogen fixation and a similar vegetative cell to heterocyst ratio. Toxin production averaged between 20-25 pmol toxin per µg protein in both treatments. Toxin composition remained constant throughout the growth cycle with the major toxins produced being neosaxitoxin (85%) and saxitoxin (15%). No evidence was obtained for the presence of either toxin GTX4 or B1. These results suggest that cultures grown in the presence of 1 mM nitrate are still utilizing atmospheric nitrogen as their nitrogen source for growth and toxin production. (This work supported by NYS Sea Grant).
PROGRESS IN THE DEVELOPMENT AND APPLICATION OF TOPOCHEMICALLY MODIFIED CELLULOSE NANOCRYSTALS. Maren Grunert and William T. Winter, Cellulose Research Institute and Department of Chemistry, 234 E. C. Jahn Lab, SUNY-College of Environmental Science and Forestry, Syracuse, NY 13210.
Īllulose is the worlds most abundant, natural, renewable, biodegradable polymer. Its molecular chains aggregate to form long threadlike bundles stabilized laterally by hydrogen bonding. In higher plants those microfibrils have a width of 2-5 nm while algal, bacterial, and tunicate cellulose form wider (15-30 nm), highly crystalline microfibrils. Due to their high potential stiffness nanocrystalline, natural cellulose fibers are gaining attention as a reinforcing phase in thermoplastic matrices.
In our efforts to better understand the factors that influence the effectiveness of this reinforcement, cellulose microcrystals from various starting materials including the tunicates Botryllus spp. and PrimacelTM (a bacterial cellulose from the Nutrasweet Kelco Company) were prepared and characterized. Using microcrystals of different sizes in composite formation can provide information about the roles of aspect ratio and specific surface area in enhancing matrix rigidity.
In a subsequent step the surface of the cellulose crystals was chemically modified by trimethylsilylation, acetylation, for example. The results of the characterization of these surface modified nanocrystals by diffraction, IR and NMR spectroscopy, and electron microscopy will be presented.
Our objective was to test the hypothesis that surface modification of the cellulose crystals might provide a route to enhanced adhesion between the particulate and matrix phases in our composites.
Acknowledgements: This work was supported by the United States Department of Agriculture (No. 9603910- WTW) and the Deutscher Akademischer Austauschdienst (MG).
LINEAR-DENDRITIC BLOCK COPOLYMERS AS NOVEL ENCAPSULATOIN AGENTS FOR POLYCYCLIC AROMATIC HYDROCARBONS. Kevin R. Lambrych and Ivan Gitsov. Polymer Research Institute, Faculty of Chemistry, SUNY College of Environmental Science & Forestry, Syracuse, NY 13210.
Amphiphilic copolymers that are capable of self-assembly into micelle systems in aqueous media have potentially important applications in environmental clean up, pharmacological, and industrial fields. The ability for linear-dendritic ABA block copolymers to encapsulate polycyclic aromatic hydrocarbons, PAH's, is analyzed in this study. Linear-dendritic architectures offer unique advantages over traditional linear copolymer architectures in that they have increased interstitial voids for the encapsulation of polyaromatic molecules placed in the intramolecular and intermolecular spaces formed by the dendritic fragment.
The linear-dendritic block copolymers investigated in this study, [G3]-PEG11,000-[G3] and [G2]-PEG5,000-[G2], are constructed of poly(benzyl ether) monodendrons as the lipophilic A block and poly(ethylene glycol) as a hydrophilic B block. Phenantrene, pyrene, perylene and fullerene (C60) are used to assess binding abilities and micellar microenvironments.
In this study [G3]-PEG11,000-[G3] and [G2]-PEG5,000-[G2] have been shown to encapsulate polycyclic aromatic hydrocarbons. These are encouraging results for the employment of novel linear-dendritic copolymers as medical delivery systems, phase-transfer agents and micro-reactors.
Two brown tide algae and a toxic red tide alga have been found to contain specific sterol biomarkers. Aureococcus anophagefferens, an alga responsible for brown tide, contains 24-methylenecholesterol and (E)- and (Z)-24-propylidenecholesterol. This is the first isolation of appreciable amounts of (Z)-24-propylidenecholesterol from an alga. The Texas brown tide alga, Aureoumbra lagunensis, contained, along with other sterols, a significant amount of 24-propylcholesterol, the stereochemistry of which was assigned to be (24R) after the unambiquous synthesis of both possible isomers. The red tide dinoflagellate Gymnodinium breve was found to also contain useful sterol biomarkers. The major sterol, 4-methyl-27-norergosta-8(14),22-dien-3-ol (47%), has never been detected before. Its structure has been determined by synthesis.
TEMPERATURE CALIBRATION FOR EXTRACTION OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) BY P.I.S.C.E.S. PASSIVE IN-SITU CONCENTRATION EXTRACTION SAMPLER. Matt Lochansky, Jocelyn Polito, Dr. John Hassett, Chemistry Department, 431 Jahn Lab, SUNY ESF.
PISCES is an acronym for a passive in situ concentration extraction sampler that can concentrate hydrophobic organic contaminants from bulk water. It is useful because organics in the environment can be present is low concentration, but still be harmful to biota. Conventional sampling techniques, like grab samples, have a detection limit too high to detect some compounds. The PISCES concentrates organics to detectable levels and are present in a matrix that is easy to analyze, an organic solvent. PISCES consists of an organic solvent in a device, with a window of polymer membrane separating the solvent from the water. A chemical potential difference drives the organic pollutants from the bulk sample, through the membrane and into the organic solvent. Increasing temperature will increase sampling rate; therefore, the samplers need to be calibrated for a variety of field conditions. In the past, temperature dependant sampling rates had been found for some organic compounds such as chlorinated benzenes and polychorinated biphenyls (PCB). Currently, calibrations are being performed for polycyclic aromatic hydrocarbons at 24°C, 18°C, and 4°C. The raw samples were analyzed by gas chromatography and quantified by a relative response factor using an internal standard. A sampling rate was calculated considering variables such as mean concentration within the tank and volume of solvent recovered. At each temperature, a specific sampling rate could be identified, independent of exposure time within a reasonable margin of error.
Mirex is a pollutant entering Lake Ontario via the Niagara River. Photochemical conversion to photomirex is one fate of this molecule. By determining the rate of this reaction and measuring the ratio of photomirex and mirex concentrations adsorbed to lake sediments, one can calculate the residence time of mirex and photomirex in the water column. To determine the reaction rate of mirex to photomirex in Lake Ontario, three pieces of information must be known: the apparent quantum yield of the reaction, solar irradiance spectra at Lake Ontario, and light attenuation at each wavelength by Lake Ontario waters. The mechanism of mirex to photomirex conversion involves the highly reactive hydrated electron, which is photoproduced within dissolved organic matter. The method by which mirex reacts is applicable to other chlorinated hydrophobic compounds such as PCBs and chlorobenzenes. Therefore, this research lays the basis for evaluating photodechlorination potential for other compounds in the Great Lakes as well as providing an independent measurement of the residence time for hydrophobic compounds.
ACTION SPECTRA FOR PHOTOCHEMICAL PRODUCTION OF HYDROGEN PEROXIDE IN NATURAL WATERS. Gary W. Miller and David J. Kieber, Faculty of Chemistry, SUNY-College of Environmental Science and Forestry, Syracuse, NY 13210; Kenneth Mopper, Faculty of Chemistry, Washington State University, WA 99164.
Hydrogen peroxide (H2O2) is ubiquitous in sunlit natural waters and is one of the major products formed from the photolysis of dissolved organic matter (DOM). Models have been developed to estimate photochemical production rates of H2O2 in natural waters. These models require, in part, wavelength dependent apparent quantum yield data for H2O2 production. Most H2O2 apparent quantum yield measurements to date have been made for fresh waters. We therefore determined apparent quantum yields for several coastal seawater samples as well as samples from Antarctica. We observed that the apparent quantum yields and activation energies were remarkably similar among diverse aquatic environments suggesting the presence of similar precursors. We are now developing an algorithm to estimate wavelength dependent apparent quantum yields for H2O2 production given spectral measurements of DOM.
METABOLIC MARKERS FOR THE DETECTION OF IRON LIMITATION IN THE BROWN TIDE ALGA, AUREOCOCCUS ANOPHAGEFFERENS. Michael F. Satchwell, Darlene B. Szmyr, Jeffrey A. Alexander, and Gregory L Boyer. State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210. (firstname.lastname@example.org, email@example.com)
Blooms of the pelagophyte, Aureococcus anophagefferens are responsible for the brown tides that occur in the Peconic Estuary on Long Island. The trace element Fe has been implicated in controlling this bloom formation. A. anophagefferens (CCMP1708) was grown in trace-metal defined artificial seawater with added iron concetrations of 0, 1, 11, 110, 1100, and 11000 nM. Cells were serially transferred through 5 culture cycles, and the several different indicators of iron limitation were examined. No difference in growth yield or growth rate, as determined by in vivo fluorescence or cell number, was observed with decreasing amounts of added iron. However two physiological indicators of iron limitation, chlorophyll per cell and Fv/Fm (e.g. DCMU-enhanced fluorescence) decreased when added iron concentrations dropped below 100 nM. The cultures did not produce siderophores as determined using the HPLC-55Fe binding assay but did have constitutive levels of ferric chelate reductase activity (2-23 nmols FeHEDTA reduced min-1 mg protein-1). This reductase activity did not increase with decreasing added iron. Low levels of added iron did induce formation of the iron-replacement protein flavodoxin. These results suggest A. anophagefferens has a low iron requirement, with the minimal iron quota between 10-20 nM. Aureococcus has developed efficient mechanisms (reductive uptake and iron-sparing) to obtain sufficient iron to support maximal growth during bloom formation. (This work was supported by New York Sea Grant)
LASER SPECTROSCOPY OF ALKOXY RADICALS AS A TOOL FOR ATMOSPHERIC CHEMISTRY. Liat G. Shemesh, Wei Deng, David R. Katz, Michael D. Lilien, Chuji Wang, and Theodore S. Dibble, Faculty of Chemistry, 440 Jahn Building, SUNY College of Environmental Science and Forestry, Syracuse NY 13210.
Alkoxy radicals are of key importance in atmospheric chemistry. The chemistry of alkoxy radicals profoundly influences low altitude ozone production both globally and in polluted environments. While the chemistry of small alkoxy radicals (< C4) has been well studied, the larger species (>=C4) have yet to be investigated directly.
We are developing laser induced fluorescence (LIF) as a monitoring tool for kinetic studies of large alkoxy radicals such as 2-butoxy, CH3CH2CH(O·)CH3. The alkoxy radicals are interrogated by a 20-nanosecond laser pulse. Molecules absorbing laser light will re-emit light (fluoresce). The color (wavelength) of the laser can be scanned over a wide range to determine the electronic spectrum unique to each species of alkoxy radical.
Reactions of alkoxy radicals produce non-fluorescing species, which lower the intensity of the LIF signal. The rate at which the LIF signal is lowered tells us the rate at which the radicals react.
We have observed LIF spectra of 2-butoxy and tert-butoxy ((CH3)3CO·). The spectral intensity is strong enough to enable us to carry out kinetics measurements. The long-term goal is to obtain general models of the kinetics of these reactions that yield accurate rate constants for alkoxy radicals. We will use the results of these studies to test and refine models of the fate of alkoxy radicals in the atmosphere.
THE PRODUCTION OF ACTIVATED CARBON AND CARBON PAPER FOR DOUBLE LAYER CAPACITORS AND FUEL CELLS. Han Liu, Suoding Li, Prithwiraj Maitra and Prof. Israel Cabasso. Polymer Research Institute, Chemistry Department, 240 Jahn Lab, State University of New York CESF, Syracuse, NY 13210.
Double layer capacitors are energy storage devices which can store more energy (20-200 times) than conventional capacitors. Since there is no chemical reaction involved, the double layer capacitors can discharge the stored energy much faster than conventional rechargeable battery and their cycle life is much longer. B.E. Conway, et al., described the application of double layer capacitor modules in EV as a load-leveling device for batteries. Similar concept can also be applied to EVs based on fuel cells. (Demonstration will be set up during the poster session to show the combination of double layer capacitors and PEM fuel cells in the EVs.)
Carbon-carbon composites have long been adopted as the major form of double layer capacitor electrodes. Without further activation treatment, the PPO polymeric carbons have high specific surface area (i.e. more than 500 m2/g), which fits the requirements for effective double layer capacitors, other energy storage devices and adsorption related applications.
The mechanism of high temperature PPO decomposition has also been studied in this lab. Modification of the PPO has been conducted to obtain the high carbon yield and best quality. Thermogravimetric Analysis (TGA), Differential Scanning Calorimeter (DSC), FTIR, and Direct Pyrolysis-MS were employed to characterize the modification and carbonization mechanisms.
Since the PPO based polymeric carbon has relatively high surface area without any further treatments, the PPO based carbon electrode has a specific capacitance of 22 F/g. The phenolic resin based electrodes performed poorly in the tests. Capacitors based on PPO carbons achieved ~60 F/g after further activation with metal hydroxides.
With high generic surface area, PPO based polymeric carbons can be readily applied in conjunction with other activated carbon materials to form high surface area electrodes. Subsequent optimizations of the activation procedure will enhance the performance further.
STRUCTURE AND BIOSYNTHESIS OF TUNICAMYCINS AND CORYNETOXINS. Billyana Tsvetanova and Neil Price, Chemistry Department, 336 Jahn Lab, SUNY-College of Environmental Science and Forestry, Syracuse, NY 13210.
Tunicamycins and corynetoxins are structurally related nucleoside analogs, respectively produced by Streptomyces lysosuperificus and phage-induced Clavibacter toxicus. Both are composed of uracil, N-acetylglucosamine (GlcNAc), and an 11-carbon dialdose called tunicamine, but differ in the nature of the N-linked acyl chain. Functionally, these compounds are transition state inhibitors of UDP-GlcNAc: polyprenol phosphate GlcNAc-1-P transferase, in which the a b -1,1'-linked GlcNAc residue mimics the GlcNAc group of the transition state. Consequently, tunicamycin and corynetoxins are potent toxins that block the first step of eukaryotic protein N-glycosylation. Soft agar overlay assays have been used to isolate tunicamycin resistant (TunR) and non-resistant (TunNR) Streptomyces lysosuperificus lines. Metabolic radiolabeling studies from precursor [14C] GlcN, [14C] acetate and [14C] uridine suggest biosynthesis via novel uridine-5'-aldehyde and UDP-4-keto-6-deoxy-N-acetylglucosamine intermediates. Tunicamycin-susceptible Bacillus overlays, HPLC-electrospray mass spectroscopy, and Matrix Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF) MS afford sensitive analysis of tunicamycin analogs and potential intermediates.
Wilcoxina produces the siderophore ferricrocin (FCR) in iron-limited culture. To study the occurrence of FCR in forest soils and in mycorrhizia-plant associates, we have prepared antibodies against FCR. Due to the small size of FCR (M.W. 711), FCR was conjugated to either bovine serum albumin (BSA) or keyhole limpet hemocyanin (KLH), to yield succinyl FCR-BSA or succinyl FCR-KLH conjugate, respectively. The succinyl FCR-KLH conjugate was used as antigen and injected into two rabbits every two weeks during 17 weeks of the boosting period. The first antisera were collected after 5 weeks of boosting, and more antisera were acquired every two weeks. The titers of antisera were determined by antibody-capture ELISA assay using succinyl FCR-BSA conjugate as antigen, and they had the values between 1,000 and 30,000. Total IgG was purified from a batch of antiserum using (NH4)SO4 precipitation and DEAE column chromatography. The identity and specificity of total IgG were studied by SDS-PAGE, dot blot, and western blot. To date, the development of a competitive ELISA assay has been unsuccessful using either antiserum or DEAE-purified total IgG. The two-antibody sandwich ELISA assay showed positive results on succinyl FCR-BSA conjugate but not with FCR itself. The total IgG will be further purified by succinyl FCR-BSA-agarose affinity column chromatography to acquire the more specific IgG. A Cr(III)-FCR complex will be prepared to produce the succinyl FCR-KLH conjugate to acquire a more specific IgG against FCR. An antibody specific to Fe(III) will be the key to develop an ELISA assay to determine siderophore concentration in roots and natural soils.
NEW ASPECTS IN ELECTROCHEMICAL SYSNTHESIS OF POLYSILANES. Xinwei Wang, Youxin Yuan and Prof. Israel Cabasso, Department of Chemistry, 239 Jahn Lab, SUNY-College of Environmental Science and Forestry, Syracuse NY 13210.
Polysilanes are a class of polymers with continuous silicon-silicon linkages in the backbone. They can be used for high resolution imaging in the lithograph industry due to their unique photochemical properties. Upon proper pyrolysis in argon, they can be converted into silicarbide, a ceramic material that can be used in high temperature environments. Electroreduction of dichlorosilanes is an alternative to the common, yet dangerous Wurtze coupling reaction in the synthesis of these polymers. The reaction scheme is shown below as
At the cathode,
At the anode,
In this study, we investigated the electrolysis of dichlorosilanes at constant current in an undivided cell based on Cu/Pt, Al/metal and H2/metal (anode/cathode) electrode combinations. Electrodes with different shapes were designed to run the electrolysis successfully. Electrolysis based on flat-sheet Cu/Pt electrodes yields mainly silane oligomers, while using Al/metal electrodes, produces oligomers as well as high polymers. A disk-like H2 electrode was made by coating a highly porous carbon with Pt. This electrode produced the polysilane only in the presence of a co-solvent, HMPA (hexamethylphosphoramide), and had slightly lower current efficiency in comparison to the Al anode. The polysilane obtained has a lower molecular weight and a narrow distribution, probably because HMPA is a poor solvent of polysilanes. Polysilanes are characterized by FT-IR, UV, fluorescence, 1H-, 13C- and 29Si- NMR, and GPC. Oligomers are studied by LC/MS.
Sinorhizobium fredii is a gram negative soil bacterium that is involved in nitrogen-fixing symbioses with leguminous plants. The symbioses occur in nodules on the plant roots, that are induced by small oligosaccharide signals called Nod factors. Sinorhizobium fredii USDA 257, a microsymbiont of soybean, secretes 6-O -fucosylated and 2-O methyl fucosylated Nod factors, and also two capsular polysaccharides; one poly Man- KDO and the other poly 2-O MeMan-KDO. Our data suggests that mannosyl and fucosyl metabolism is linked in this bacterium, and that 2-O methylation requires S-adenosylmethionine as a cofactor. D-Mannose is generally synthesized as Man-6-phosphate from D-fructose-6-phosphate by phosphomannose isomerase (PMI). However, we noted that the Sinorhizobium PMI is unique and shows sequence homology to only one other protein - mammalian liver renin-binding protein (RnBP). RnBP functions by activating renin but also has a D-N-acetylmannosamine 2-epimerase activity that interconverts D-ManNAc and D-GlcNAc. We hypothesize that the Sinorhizobium PMI may also be a ManNAc 2-epimerase. This might allows Sinorhizobium to overcome the potential inhibition of PMI by endogenous 2-O-methymannose.
The endeclomycorrhizal species Wilcoxina mikaloe produces the siderophore ferricrocin (Figure 1) in response to iron limitation. The siderophore chelates and transports iron via specific transport systems to promote cell growth. The deferri-ferricrocin also binds metals other than iron to form complexes. Deferri-ferricrocin was first purified, then used to prepare the chromium, aluminum, and gallium complexes. These complexes were detected by HPLC coupled with mass spectroscopy (LCMS). Their apparent stability decreases in the sequence of chromium, aluminum, and gallium. In order to study the effect of aluminum on the production of siderophores in Wilcoxina mikolae, the fungus was cultured under different levels of aluminum. The culture supernatant was collected and analyzed by both HPLC with radioactive detector and LCMS. Both results showed that aluminum inhibited the production of siderophore. This effect varied depending on different level of aluminum and iron present in the media. Similar studies on copper and zinc are in progress.
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Last modified July 19, 1999